Pictorial indicator



Patented May 18, 1954 UNITED OFFICE PICTORIAL INDICATOR William C.Hartman, Levittown, N. Y., assigner to The Sperry Corporation, GreatNeck, N. Y., a

corporation of Delaware 15 Claims.

This invention relates to pictorial indicators, and in particular, top-ictorial indicators for continuously indicating the position of amobile craft relative to a reference station.

in copending application S. N. 195,761, iiled November l5, 1950,entitled Aircraft Navigation System, and assigned to the same assigneeas the present application, a pictorial indicator is disclosed forcontinuously indicating the position of a mobile craft relative to areference ground station. This pictorial indicator includes a circulartable adapted to carry a inap of the terrain surrounding the referencestation. A carriage is supported above the map table for radial motionthereover on guide means such as a .pair of parallel rods forming atrack. The carriage is automatically positioned alongI the trackrelative to the center of the map by a suitable radio distance measuringequipment and a servo control system in accordance with changes indistance between the mobile craft and the reference station. The trackis supported from a decl: situated below the map table, and the deck isautomatically rotated about an axis extending through the center of themap table by suitable radio bearing determining apparatus and a servocontrol system in accordance with the bearing of the mobile craftrelative to the refrence station. A member attached to the carriage forrepresenting the mobile craft is thus positioned along with the carriageover the upper surface of the map in polar coordinates, the center ofthe map denoting the reference ground station.

It is desirable in navigational pictorial indicators of the above typeto display and to permanently record the path followed by a mobile craftwith a minimum of obstruction to the viewing surface of the and withmaximum compactness in the indicator. it is also desirable to providesimple mechanisms for continuously indicating the path followed by amobile craft and to provide for the rapid change of maps as the mobilecraft moves from one reference station to another. Furthermore, it isimportant that the position oi the mobile craft be indicated in truepolar coordinates as radial distance from an angle about the center ofthe inap.

Certain prior qictorial indicator systems, while indicating andrecording the values of two variables in true polar coordinates,obstruct certain portions of the viewing surface of the map or chart.Other known types of polar coordinate indicator systems such as cathoderay indicators 're not suitable for providing a permanent record of thevalues of the two variables being indicated. While there exists one typeof prior indicator system which does not have the obstruction problemand does provide a permanent record of the values of two variables, itdoes not indicate the values of these variables in true polarcoordinates. This latter system indicates the value of one of theVariables as distance from the center of a chart along an arcuate lineextending from the center to the edge of the chart.

Accordingly, an object of the present invention is to provide animproved ypictorial indicator.

Another object of the invention is to provide a pictorial indicatorsuitable for displaying and permanently recording on a map the pathfollowed by a mobile craft as it moves relative to a reference stationwith a minimum of obstruction to the viewing surface of the map.

Still another object of the invention is to provide a navigationalpictorial indicator including a path tracingI system for denoting craftposition on a circular table with a minimum of obstruction, and With thetable and path tracing system arranged for maximum compactness of theindicator for all craft position indications.

Yet another object of the invention is to provide a reference table witha movable member thereabove controlled according to the position of amovable body therebelow, Without passing any intercoupling elementsthrough the reference table.

In accordance with the present invention there is introduced an improvedpictorial indicator for indicating the values of tivo variables in truepolar coordinates. The indicator includes a circular table suspendedadjacent to and separated from a rotatable platform. The table and theplatform are adapted for relative motion therebetween about an axisextending through the center of the table. The rotatable platformcarries a linearly movable body situated in the spacebetween the tableand the platform. rThe movable body is positioned along a radial linefrom the axis according to one variable, and is positioned along withthe rotatable platform about the axis according to the other variable.The movement of the body is transferred from below the table into themovement of a ducial point on a member above the table by a mechanicallinkage.

The vmechanical linkage includes first and second arms pivoted togethernear the edge of the table and located between the lower or rear surfaceoi the table and the rotatable platform. The first arml is furtherpivo'ted at the axis and the second arm is further pivoted at themovable body. One end of the member adapted for movement over the upperor front surface of he circular table is rigidly attached to the secondarm near the pivot position of the rst and second arms. A iiducial pointnear the other end of the member is situated over the upper surface ofthe table at a position corresponding to the pivot position of thesecond arm on the movable body adjacent the lower surface of the table.The fiducial point on the member adjacent to the upper surface of thetable moves over the surface of the table as distance from and angleabout the center of the table in true -polar coordinates in accordancewith the move ment of the movable -body adjacent the lower surface ofthe table.

The above objects of and the brief introducY tion to the presentinvention will be more fully understood and further objects andadvantages will become apparent from a careful study of kthe followingdetailed description in connection with the drawing, wherein:

The single figure of the drawing shows a schematic perspective diagramof the pictorial indicator of the invention as employed in conjunctionwith suitable radio navigational aids to indicate the position of amovable craft relative to a reference station, and in conjunction with acompass to indicate the crafts heading.

Referring to the single figure, the pictorial indicator and radionavigational aids may be en,- ployed in a mobile craft, as for example,an aircraft, to provide a continuous indication of the crafts positionin bearing and distance relative to a reference station, such as theCivil Aeronautics Administrations Omni-Bearing Distance (OBD) groundstation. The radio navigational aids include a conventional bearingreceiver for determining the bearing of the aircraft relative to the OBDstation, and a conventional distance measuringr equipment fordetermining the distance between the aircraft and the OBD station. Inaddition, tne aircrafts heading may be determined by a compass ordirectional gyroscope, and displayed by the pictorial indicator asdirection of a small heading arrow. Bearing, distance and headinginformation is supplied continuously to the pictorial indicator of thepresent invention as angular position of three separate shafts.

The bearing of the aircraft is measured by the conventional bearingreceiver Il, which receives bearing determining signals from the OBDground station over antenna i2. Bearing information is provided at theoutput of receiver il as angular position of shaft i3, and the angularposition of this shaft is transferred by a conventional servo systeminto corresponding angular position of a remote shaft l@ for actuatingthe pictorial indicator.

The servo system comprises a synchro generator l5 whose rotor ismechanically coupled to shaft I3. The single winding of synchrogenerator i5 is excited by a fixed reference voltage Er, such as a 400cycle line voltage, and its multiple winding system is electricallyconnected to the multiple winding system of a control transformer IB.The rotor of control transformer i6 is mechanically coupled to shaft l lwhich is positioned by the servomotor i l through reduction gears I8.The output error control voltage across the single output winding ofcontrol transformer I5, whose reversible phase and magnitude is determined by the relative angular displacement be tween the positions ofshafts i3 and i4, is amplied by amplifier I9 and applied to servomotorI1. The servomotor I7, which may be of the twophase type and thus issupplied with a fixed voltage ES in phase quadrature with voltage Er,rotates shaft Hi through the reduction gears I2 until its angularposition conforms with the angular position of shaft i3, therebyreducing the output error control voltage to zero.

The distance between the aircraft and the ground station is measured bya conventional distance measuring equipment 2D, which initiates andreceives distance determining signals from the OBD ground stationresponder over antenna 2 I. Distance information is provided at theoutput of equipment 20 as angular position of a shaft 22, and theangular position of this shaft is transferred by a conventionalpotentiometer servo control system into corresponding angular positionof a remote shaft 23 for actuating the pictorial indicator Athrough amechanical differential 24.

The servo system comprises first and second potentiometers havingresistance windings 25 and 23 respectively. The lower terminal of eachof these windings is electrically connected to a common ground terminal.The upper terminal of winding 25 is supplied with a reference voltagefrom one-half of the secondary winding of transformer 2'?, and the upperterminal of winding 26 is supplied with a reference voltage of oppositephase from the other half of the secondary winding of transformer 2l,the center tap of the secondary winding being connected to the commonground terminal. The primary winding of transformer 2l' is energized bythe reference voltage Er.

The wiper arm 28 of the first potentiometer is mechanically coupled toshaft 22 and electrically connected through a series resistor 29 to arst input terminal of amplifier 38. r.he second input terminal ofamplifier 30 is connected to a common ground terminal. The wiper arm 3lof the second potentiometer is mechanically coupled to shaft Y23 andelectrically connected through a series resistor 32 to the first inputterminal of l amplifier 30.

The angular position of shaft 23 conforms with the angular position ofshaft 22 when wiper arm 3l extends in a direction parallel to thedirection of wiper arm 28. For this condition, the output voltagebetween arm 28 and ground is equal in magnitude and opposite in phase tothe output voltage between arm 3i and ground, and the resulting errorcontrol voltage across the input terminals of amplifier Si! is zero.When the angular positions of shafts 23 and 22 are initially displacedrelative to each other, an error control voltage is developed across theinput terminals of amplifier 3) whose phase and magnitude is determinedby the relative angular displacement. This control voltage is ampliedand applied to servomotor 33 to rotate shaft 23 through reduction gears3d and slip clutch 35 in a direction to bring its angular position intoagreement with the angular position of shaft 22. Servomotor 33 issupplied with a reference voltage Es in phase quadrature with thevoltage Er.

A cam 3S is mounted on and pinned to shaft 23 to serve as a limit stopwhen it is driven against stop pin 31 at each end of the travel of arm3| of the second potentiometer.

The heading of the aircraft is determined by its own compass system 38,which may include a directional gyroscope, and this information isprovided as the angular position of a shaft 39 ae'zaoss coupled to thecompass. The angular position of shaft 33 is transferred by aconventional servo system into corresponding angular position of aremote shaft its for actuating the heading arrow of the pictorialindicator.

The heading servo system coupled between shafts 33 and Lid and includinga synchro generator fill, a control transformer E2, an amplier 355, aservoniotor and reduction gears 45, may be identical to the servo systemcoupled between shafts i3 and lil as shown and described in the bearingchannel.

The pictorial indicator of the present invention comprises a platform 5lsupported by a hollow shaft El. extending through main bearing 53. Theplatform 5! is adapted for angular movement about the longitudinal axisA-A of hollow shaft A small ring gear @Ll is attached to the outsidesurfaceJ and near the lower end of hollow shaft and is driven by spurgear 55 attached to the upper end of shaft I4' extending through bearing5E.

A thin circular table 5l is suspended above platform 5i by threesupporting columns or posts 53, 5B and Eil rigidly attached to theplatform. Three dise rollers Si, t2 and 63 are pivoted atop posts 59 andEl?, respectively, for rotation about a longitudinal axis parallel toaxis A-A. These rollers have rounded edges for engaging the groovedinner periphery of a ring gear 64, thus sup-porting the ring gear forangular rotation about axis lli-A. Table 5l is attached to and supportedby the ring gear @il in such a way that axis A--A passes through thecenter of the table.

The table may be rotated about axis A-A independently of any motion ofplatform 5I by rotating crank 5e situated below the platform andattached to one end of a shaft 56. Shaft B extends through a bearing 5lto a worm element engaged with worm wheel 69 for driving a shaft A spurgear ll attached to shaft 'l0 drives a rinfr l2. The ring gear 12 issupported for rotation about axis A-A and is retained in position byretaining rollers schematically illustrated at 'i3 and lil.

Rotation of ring gear 'l2 about axis A-A drives a shaft i5 through spurgear 1li, the platform 5i remaining stationary due to the reductiongears lil between shafts lil', l@ and motor H. Shaft 'l5 extends in adirection parallel to axis A--A through platform 5l. It is supported atthe platform 5l by a bearing l1. Spur gear l'S attached to the upper endof shaft 'l5 rotates the ring gear til on the rollers di, B2 and E3, thetable supported by this ring gear about airis AMA. Thus, rotating crank65 causes ring gear if: table lll to be-rotated in unison Withoutimparting any movement to platform 5I.

While one revolution of table 5l and ring gear 54 is produced for eachrevolution of ring gear l2, as illustrated in the single ligure, thisspecific relationship is not necessary. The table 51 could be rotatedeither faster or slower than the angular rot ion of ring gear 'i2 ifdesired, according to the ratios of gears 'i6 and 'i8 with theirrespectively ineshed ring gears.

The platform 5i is also rotatable about axis A-A without impartingmovement to table 5l. Rotation of platform about axis A-A causes shaftl5 to rotate within its bearing 'il as it is carried by the platformaround axis A-A. The ring gear 'l2 is held stationary by the holdingaction. of the worm gear e8 and ES thus preventingtable 5l from movingas spur gear 'i8 travels about the periphery of ringgear 64. Spur gear'it also travels about the periphery of ringgear 'l2 and passes over thetop of spur gear 1I.

Table 5l is adapted for supporting a circular map of the terrainsurrounding a selected OBD ground station. The map may be attached tothe upper surface of a detachable circular plate 1Q, and the circularplate may be sloted or keyed, as at 'l, so that when placed upon table51 it can be quickly oriented to a predetermined reference position andfastened to the table.

The angular position of shafts it and I4', varying according to changesin the bearing of the ircraitr relative to the 013D station, determinesthe angular position of platform 5| about axis A-A. 250 degree change inthe aircrafts bearing turns shafts lil, is', and. platform 5IV throughexactly one revolution. Shaft is', therefore, is one input to thepictorial indicator, and

'its angular position varies directly according to one of the variablesto be indicated.

The angular position of shaft 23 represents another variable to beindicated, i. e. the distance between aircraft and OBD station. Shaft 25drives shaft 23 which in turn is coupled through mechanical differentialit to shaft systein and shaft system lo passes through bearing ti 'todrive a hollow shaft 82 through spur gears 33 and tl. Hollow shaft 82 iscoaxially aligned and supported within hollow shaft 52 and isindependently rotatable therein about axis A-A, This hollow shaft d2extends through an opening in platform 5l to a pinion 85 attached to itsupper end. Pinion Se is engaged with a rack et that is linearlyslide-ble over the surface of platform til and against a rear guidingsurface 5l. The racl: 3e is held in alignment against guiding surface 3land the surface of platform lil by guides schematically illustrated at38 and 3S.

body or block il@ is rigidly attached near one end of rack @t formovement therewith over the surface of the platform 5i. The body Si@ isso shaped and arranged that it can be translated from near the edge ofthe platform 5l to a position directly above the ifi-A. A shaft 3|v ispivota-lly mounted in a bearing on top of block lit at a location suchthat when bloolz Sii is translated to a position directly above axisA--A, the longitudinal of shaft @i coincides with the axis AMA.lvloreover, bloei: @il is translated along with rack Stover the surfaceof the platform, the shaft Bl translated along a radial line extendingfrom A--A toward the edge of the platform according to' the distancebetween aircraft and the reference ground station. Si. ce the radiusvector from axis A-A to shaft ill is rotated along with platform 5labout A--A in accordance with the bearing of the aircraft relative tothe ground station, the position at which shaft Si is situated at anyinstant thus represents the position of the aircraft in true polarcoordinates relative to the axis :lf-A.

For changes in the aircrafts bearing while distance is constant, themechanical difierential fil prevents the angular rotation of platform 5iabout A-A from translating the raolr. llt along the surface of theplatform, The different'al prevents movement rotating hollow shaft 'ft2in. the saine direction and at ne angular velocity as hollow shaft 52,when shaft system is at rest. The rack d3 pinion Sli thus remain in thesaine relative positions as though the platform 5l were stationary.

With changes in the aircrafts distance while bearing is constant, theshaft i4 and platform 5| remain stationary, and shaft 23 drives shaftsystem 80 through differential 24, thus translating the body Se on rack86 relative to axis A-A according to the changes in distance between theaircraft and ground station.

The vector position of shaft El relative to axis A-A is transferred frombelow table 51 to the upper surface of the table by a mechanical linkageincluding an arm S2 pivoted at one end through a bearing to shaft 9i.The other end of arm 32 is attached and pinned to a shaft g3 extendingparallel to axis A-A and situated just beyond the edge of table 51.Another arm 94 has one of its ends pivoted through a bearing to thelower end of shaft 93 and its other end pivoted. through a bearing toshaft 95 extending through the center of hollow shaft 32. The lon-'gitudinal axis of this shaft 95 is the axis A-A.

One end of a curved member $6, preferably formed of rigid transparentmaterial, is attached and pinned to the upper end of shaft 93 whichextends slightly higher than the upper surface of table 5l. This memberis adapted for parallel movement over the upper surface of table 51, andis so aligned that a fiducial point near its other end is situateddirectly above shaft 9|. Moreover, the longitudinal axis of shaft 9|extends through this fiducial point.

Member S6 moves over the upper surface of table 51 in the same manner inwhich arm 92 moves below the table since they are rigidly joinedtogether. The distance between the longitudinal axis of shaft 9| and thelongitudinal axis of shaft 93 is exactly equal to the distance betweenaxis A-A and the longitudinal axis of shaft S3. Thus, the fiducial pointon member 86 made to move over the upper surface of table 51 in truepolar coordinates about the center of table 51 when shaft e! moves intrue polar coordinates about axis A-A below the table.

The transparent member 58 is the only necessary part of the indicatorthat appears over the front surface of the map. Being transparent, itcauses substantially no obstruction to the maps viewing surface. Itsrigidity enables a small stylus S5 to be mounted at the fiducial pointfor tracing upon the surface of the map the path followed by theaircraft as it moves in the vicinity of the reference ground station.

The heading of the aircraft may be indicated by the pictorial indicatoras direction of a small heading arrow S1 which is shown pivoted onmember te at the fiducia-l point. This heading arrow S1 comprises a barmagnet, and its direction is determined by a magnetic field produced bya further permanent magnet 98 situated directly below the heading arrowand adiacent to the lower surface of table 51. Table 51 and circularplate 19 are constructed of non-magnetic material to allow for magneticcoupling between inagnet Q8 and arrow 91. The magnet 98 is attached tothe upper end of shaft 9| for rotation in unison therewith about thelongitudinal axis of the shaft.

Shaft 9i is rotated about its longitudinal axis by a mechanical gearsystem coupling this shaft to shaft S5, and both shafts 9| and 95 rotatein the same direction and at the same angular velocity. Bevel gear 90pinned to shaft 9i is engaged with bevel gear 09 mounted to body 90 bymeans of a hollow bearing through which is passed a splined shaft iii.rThe splined shaft |0| is supported at each end by bearing blocks 8, |02and |03 mounted on platform 5|, and the longitudinal axis of this shaftIUI extends in a direction perpendicular to axis A-A and along a radialline parallel to the sliding surface 81. Bevel gear |00 is keyed inorder that it may be slid over the surface of shaft |0| and also bedriven by the rotation of shaft |0|. Splined shaft l0! is rotated by theshaft 95 through additional bevel gears |04 and |05, and shaft 95 isdriven by the shaft 40 passing through bearing |06 to the spur gears |01and 08, and idler gear |09.

The bevel gears 9S and |00 have a one-to-one ratio as do bevel gears weand |85. Thus, one revolution of shaft produces one revolution of shaft9| and, likewise, one revolution of heading arrow 91. Moreover, themechanical gear system operates as a differential to rotate shafts 9|and |0| when platform 5| is rotated about axis A-A and shaft S is atrest. For example, with a fixed heading, i. e., shafts 40, 40 and 95being held stationary, and' a changing bearing, the platform 5| rotatesabout axis A-A to indicate the change in bearing and this rotationdrives shaft It! through the bevel gears |04 and |05. rilhe rotation ofshaft lill drives shaft 9| through an angle exactly equal to the anglethrough which platform 5| is rotated but opposite in direction, and thismotion of shaft 9| is such as to maintain the direction of heading arrow91 fixed, thus indicating a xed heading.

While, for the purpose of illustration, the pictorial indicator of thepresent invention has been shown and described in conjunction withsuitable radio navigational aids for indicating the position of a mobilecraft relative to a reference station, it is by no means limited to thisspecific use. The pictorial indicator may be employed to indicate thevalues of any two variables in polar coordinates where the values of thetwo variables are in a form which can be supplied to the indicators twoinput shafts.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A pictorial indicator for continuously indieating the position of amobile craft relative to a reference station, comprising in combination,a platform supported by said craft and rotatable about an axis, meansfor varying the angular position of said rotatable platform about saidaxis according to the bearing of said craft relative to said referencestation, means including a body situated on said rotatable platform andmotive means coupled thereto for providing translational motion of saidbody along a radial line from said axis according to the range of saidcraft from said reference station, a table suspended above said platformand adapted for supporting upon its upper surface a map of the terrainsurrounding said reference station, a mechanical linkage comprisingfirst and second arms pivoted together and situated in the space betweensaid table and said platform, said first arm also being pivoted at saidaxis and' said second arm also being pivoted at said movable body, and athird arm situated above the upper surface of said map table forparallel movement thereover, said third arm having one end rigidlyioined to said second arm for movement therewith, the other end of saidthird arm being positioned over said map table and being located at aposition with respect to said map Vtable corresponding to the pivotposition of said second arm on said movable body, whereby the movementof said body according to the bearing and range of said craft relativeto said reference station is transferred into movement of a ducial pointnear the other end of said third arm over the upper surface of said maptable as bearing and range of said craft relative to the center of saidmap table.

2. A pictorial indicator` for continuously indicating the position of amobile craft relative to a reference station, comprising in combination,a platform supported by said craft and rotatable about an axis, meansincluding a body situated on said rotatable platform and motive meanscoupled thereto for providing translational motion of said body along aradial line from said Yaxis according to the range of said craft fromsaid reference station, a table suspended above said platform andadapted for Supporting upon its upper surface a map of the terrainsurrounding said reference station, means for varying the angulardisplacement between said table and said platform about said axisaccording to the bearing of said craft relative to said referencestation, a mechanical linkage comprising iirst and second arms pivotedtogether and situated in the space between said table and said platform,said first arm also being pivoted at said axis and said second arm alsobeing pivoted at said movable body, and a third arm situated above theupper surface of said map table for movement thereover, said third armhaving one end rigidly joined to said second arm for movement therewith,the other end of said third' arm being positioned over said map tableand being located at a position with respect to said map tablecorresponding to the pivot position of said second arm on said movablebody, whereby the movement of said body according to the bearing andrange of said craft relative to said reference station is transferredinto movernent of a ducial point near the other end of said third armover the yupper surface of said map table as bearing and range of saidcraft relative to the center of said map table.

3. A pictorial indicator for continuously indicating the position of amobile craft relative to a reference station, comprising in combination,a platform supported by said craft and rotatable about an axis, meansincluding a body situated on said rotatable platform and motive meanscoupled thereto for providing translational motion of said body along aradial line from said axis according to the range of said craft fromsaid reference station, a table suspended above said platform andadapted for supporting upon its upper surface a inap of the terrainsurrounding said reference station, means for Varying the angulardisplacement between said table and said rotatable platform about saidaxis according to the bearing of said craft relative to said referencestation, a mechanical linkage comprising iirst and second arms pivotedtogether and situated in the space between said table and said platform,said rst arm also being pivoted at said axis and said second arm beingfurther pivoted at said movable body, a member rigidly attached to saidsecond arm and extending in a direction parallel to said axis, saidmember projecting slightly higher than the upper surface and beyond therim of said map table, and a third arm situated above the upper surfaceof said map table Vand having one end rigidly joined to .said member,said third arm being positioned for movement over said map table, theother end of said third arm being located at a position with respect tosaid map table corresponding to the pivot position of said second arm onsaid movable body, whereby the movement of said'body according to thebear-ing and range of said craft relative `to said reference station istransferred into move.- rnent of a fiducial point near the other end ofsaid third arm over said map table as bearing and range of said craflJrelative to the center of said map table.

e. The apparatus as donned in claim 3, wherein said third arijn situatedabove the upper .surface of said map table for movement thereovercomprises a heading indicator pivoted at the other end of said third armat said fiducial point, and means including a rotatable element on saidbody for positioning said heading indicator in accordance with theheading of said mobile craft.

5. rThe apparatus as defined in claim fi, wherein said heading indicatorpivoted at the other end of said third arm includes a permanent magnet,and said means for iiiositioninfr said heading indicator includes afurther permanent magnet located beneath said table and pivoted on saidbedr.

d. The apparatus as defined in claim 3 wherein said third arm situatedabove the upper surface of said inap table for movement thereover iscurved tc conform with the curvature at .the rim of said map table.

7. rThe apparatus as defined in claim 3, whereu in said third armsituated above the upper surface of said map table for movementthereover is formed of rigid transparent material.

8. The apparatus as defined in claim 3 wherein said third arm situatedabove the upper surface of said map table for movement thereoverincludes a stylus attached to the other end of said third arm at saidnducial point, said stylus being adapted for tracing the position ofsaid mobile Vcraft on said map table in accordance with the range andbearing of said mobile craft relative to said reference station.

' i?. rEhe apparatus as dei'lned in claim 3 further including means forpositioning said map table relative to said craft independently of theposition of said platform.

l0. A pictorial indicator for continuously indieating the values offirst and second variables including a body movable in a plane accordingto said first and second variables, comprising an indicatortable havinga lower surface suspended adjacent said movable body, said table lyingin aplane parallel to the plane of movement of said movable body7 meansincluding a mechanical linkage situated below said table and havingfirst and second arms pivoted together about a rst axis perpendiculartothe plane of said table, said first arm being further pivoted at asecond axis paralell to and separated from said rst and said second armbeing furtheln pivoted at said movable body, said pivotal connectionabout said iirst axis being substantially equidistant from said secondaxis and said pivotal connection on said movable body, and a rigidmember fixedly connected to said second arm in the region of saidpivotal connection about said first axis and extending therefrom andoutside the perimeter of said table to a position over the upper surface0f said table directly above said movable body 11 for transferring themotion of said movable body below said table into movement of a fiducialpoint near the end of said rigid member over the upper surface of saidtable.

1l. In combination, a circular disc table, a rst arm beneath said tablepivoted about the axis of symmetry of said table, a second arm beneathsaid table pivotally connected to said first arm about an axis parallelto said axis of symmetry and at a distance from said axis of symmetryslightly greater than the radius of said table, a movable body beneathsaid table connected to said second arm, the pivotal connection betweensaid iirst arm and said second arm being at substantially equaldistances from said axis of symmetry and said connection to said body;and a rigid member xedly connected to said second arm in the region ofthe axis of the pivotal connection between said first and second armsand extending therefrom to a position over said table directly abovesaid body and thereby substantially duplicating over the surface of saidtable the plan position of said body therebelow.

12. A mechanism comprising, a body movable in angular position about anaxis and movable along a radial line perpendicular to said axis, a tablehaving an upper and a lower surface, said lower surface suspendedadjacent to said movable body, a member situated above the upper surfaceof said table for movement thereover, means for transferring the motionof said movable body beneath said table into movement of said memberabove the upper surface of said table, said means including amechanica-1 linkage having first and second arms pivoted together andsituated beneath said table, said first larm being further pivoted atsaid axis, and said second arm being further pivoted at said movablebody, and means rigidly joining one end of said member above the tableto said second arm below said table for movement therewith, the otherend of said member being located at a position over the upper surface ofsaid table directly above said movable body whereby the movement of afiducial point on said member above said table in angle about anddistance from said axis varies according to the movement of said movablebody beneath said table in angle about and distance from said axis.

13. In combination, a body movable in angular position about -an axisand movable along a radial line perpendicular to said axis, a circulartable having an upper and a lower surface, said lower surface suspendedadjacent to said movable body, the center of said circular tablecoinciding with said axis, -a member situated above the upper surface ofsaid table for movement thereover, means for transferring the motion ofsaid movable body beneath said table into movement of said member abovethe upper surface of said table, said means including an arm situatedbeneath said table, means pivotally connecting a rst point on said armto said movable body, means pivotally connected to said arm at a secondpoint remote from said rst point for maintaining said second point at afixed radial distance from said axis, and means rigidly joining one endof said member above the table to said arm below said table for movementtherewith, the other end of said member being located at a position overthe upper surface of said table directly above said movable body wherebythe movement of a ducial point on said member above said table in angleabout and distance from the center of said table varies according to themovement of said movable body beneath said table in angle about anddistance from said axis.

14. The apparatus as defined in claim 13 wherein the distance betweenthe second point on said arm and said axis is equal to the distancebetween the rst a-nd second points on said arm.

15. A pictorial indicator for continuously indicating the position of amobile craft relative to a reference station including movable meansvariable in angular position about an axis according to the bearing ofsaid craft relative to said reference station and variable in positionalong a radial line from said axis according to the range of said craftfrom said reference station, comprising a circular table adapted forsupporting upon its upper surface a map of the terrain surrounding saidreference station, said table lying in a plane perpendicular to saidaxis and having its lower surface situated adjacent to said movablemeans, the center of said table coinciding with said axis, a membersituated above the upper surface of said table for parallel movementthereover, means for transferring the motion of said movable meansbeneath said table into movement of said member above said table, saidmeans including a mechanical linkage having rst and second arms pivotedtogether near the rim of and beneath said table, said rst arm beingfurther pivoted at said axis and said second arm being further pivotedat said movable means, shaft means situated at a distance from said axisslightly greater than the radius of said table and extending in adirection parallel to said axis and projecting slightly higher than theupper surface of said table, one end of said shaft means rigidly joinedto said second arm beneath said table and the other end of said shaftmeans joined to one end of said member above said table, the other endof said member being located at a position over the upper surface ofsaid table directly above said movable means whereby the movement of aliducial point on said member above said table in angle about anddistance from the center of the table varies according to the movementof said movable means beneath said table as angle about and distancefrom said axis.

References Cited in the file of this patent UNITED STATES PATENTS Number

